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  1. Member E1or0's Avatar
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    #1

    Default Does HUBS use ip addresses?

    I know it might sound dumb this question guys but as I'm studying with a couple of friends this question came to discussion, one of the guys stated that he went to a premise where his client had only a hub no router in between just the hub connecting several computers lets say 7 with static ip address assign, only 3 of them had the same ip address manually assign he was getting a pop up windows saying that there was a conflict of ip address i would say,

    don't hubs and switches go by mac addresses ???
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  3. Senior Member blackninja's Avatar
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    #2
    Hubs and switches operate at layer 2 but the computer still needs a layer 3 address to talk to other computers.

    So on 7 computers on a hub, they would need 7 different IP addresses,which are in the same subnet.

    Computer A transmitting to B would broadcast the frames to every port (except the one it came out of) and on the port computer B is attached will be the only one to accept the frames.

    Learn about ARP.
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  4. cisco noob fly351's Avatar
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    #3
    No they do not. Hub's operate at layer 1. They are just a multi-port repeater. Switches operate at layer 2 which forward/filter based on the hardware address (eq MAC address).
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  5. Senior Member blackninja's Avatar
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    #4
    Quote Originally Posted by fly351 View Post
    No they do not. Hub's operate at layer 1. They are just a multi-port repeater. Switches operate at layer 2 which forward/filter based on the hardware address (eq MAC address).

    Ohh.....my bad. Tired.

    But I'm sure you knew what I meant, just a little boo boo.
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  6. cisco noob fly351's Avatar
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    #5
    lol yah I do. My post probably sounds as if it is directed to you but I actually was typing it before you replied
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  7. Member E1or0's Avatar
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    #6
    I know that hubs operates at layer 1

    now the tricky question something i cant still understand is if hubs forward every frame to every port and only the destination host will accept the frame base on its mac address, why does every host still need an ip address in order to comunicate? since hubs are not layer 3 devices
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  8. Went to the dark side.... Moderator networker050184's Avatar
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    #7
    The hub doesn't operate at L3 but the host does. Think of how a host gets data to another. It first needs the destination IP address (via DNS, manually telling it etc.). Then it uses arp to get the L2 address. If it didn't have a destination IP address how could it arp for the other ends MAC?
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  9. The Colosus of Clout Paul Boz's Avatar
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    #8
    Think of computers as layer 3 devices. Because computers speak in terms of IP addresses ARP exists to translate layer 3 IP addresses to layer 2 MAC addresses. Computers may need to be globally accessible so IP addressing is a must. As others have said, hubs don't use IP or MAC addresses. They just mirror everything from every port to all other ports.

    Think of it this way. A computer can't just say "hey I want to send this data over to that computer over there." It has to be more specific by specifying an address.
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  10. Member E1or0's Avatar
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    #9
    Networker that explanation makes perfect sence, there is not way for arp to get a mac address of a device without that device having an ip address assign - now i get it

    blackninja
    fly
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    pauk - very good as well, i always see computers as layer 3 devices

    thank you all for your time
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  11. cisco noob fly351's Avatar
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    #10
    Quote Originally Posted by E1or0 View Post
    very good as well, i always see computers as layer 3 devices
    Just remember... computers operate on all layers
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    #11
    Quote Originally Posted by fly351 View Post
    Just remember... computers operate on all layers
    Yea, I was going to say, Paul's computer must suck. I use an L7 computer that has applications.

    (We actually just gave him an old Linksys switch with a Fischer-Price front-end. It's been keeping him busy for hours.)
    Last edited by dynamik; 06-22-2010 at 06:04 PM.
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  13. Member E1or0's Avatar
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    #12
    Think of computers as layer 3 devices. Because computers speak in terms of IP addresses ARP exists to translate layer 3 IP addresses to layer 2 MAC addresses. Computers may need to be globally accessible so IP addressing is a must. As others have said, hubs don't use IP or MAC addresses. They just mirror everything from every port to all other ports.

    Think of it this way. A computer can't just say "hey I want to send this data over to that computer over there." It has to be more specific by specifying an address.
    They just mirror everything from every port to all other ports.
    Quick question that came to my attention just about now, does hubs use ARP in order to get a mac address of a host? I always thought only switches can do this
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    #13
    Hubs do not. They're layer-1 and just repeat electrical signals.
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  15. Senior Member phantasm's Avatar
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    #14
    Quote Originally Posted by E1or0 View Post
    They just mirror everything from every port to all other ports.
    Quick question that came to my attention just about now, do hubs use ARP in order to get a mac address of a host? I always thought only switches can do this
    Ok, after that correction I would suggest you read up on ARP and RARP.
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    #15
    Just think of a HUB as a multi-port repeater. It's job is to clean up a signal and send it back out on the physical medium. Why would you do this? Normally you don't see them used too much anymore it's mainly switches you see used for the most part. But, say you have a distance that exceeds the specifications of your medium, you could implement the hub to connect your medium, then have medium going out the other side, to "extend" the length of your path. Make sense?


    That's all a hub does. Remember as well, if you are using a hub, all connected device use shared medium, since all devices that are connected are in the same collision domain, unlike a switch, where each device is in its' own collision domain and has it's own bandwidth. What I mean for example,
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  17. Member E1or0's Avatar
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    #16
    Originally posted by Networker
    The hub doesn't operate at L3 but the host does. Think of how a host gets data to another. It first needs the destination IP address (via DNS, manually telling it etc.). Then it uses arp to get the L2 address. If it didn't have a destination IP address how could it arp for the other ends MAC?
    --------------------------

    Originally posted by Dinamik
    Hubs do not. They're layer-1 and just repeat electrical signals.
    --------------------------

    It seems like some of you guys have doubs about the question wether hubs use ARP or not, if Hubs don't use ARP every host connected to the HUB wont neccesaryly need an ip addresses assign correct ?

    Me personally I don't think hubs use ARP to get to a host, a hub is just a repeater the Host is the one building the frame with its source and destination mac address, that frame will eventually get to its destination once it arrive at the designated host, there is no need for ip address to be involve

    I think the only reason that hosts connected to a hub uses ip addresses is so that group of hosts can be found under a specific subnet or if they are connected to a switch Am I wrong or right?

    I'm still a noob on this guys have patience with me

    Thank you
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  18. Went to the dark side.... Moderator networker050184's Avatar
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    #17
    Dude, forget ARP and hub in the same sentence . A hub simply regenerates the incoming electrical signal and sends it out all the other ports. It doesn't care what that signal is.
    An expert is a man who has made all the mistakes which can be made.
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  19. Senior Member alan2308's Avatar
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    #18
    Quote Originally Posted by E1or0 View Post
    It seems like some of you guys have doubs about the question wether hubs use ARP or not, if Hubs don't use ARP every host connected to the HUB wont neccesaryly need an ip addresses assign correct ?
    Hubs don't "use" anything, they just regenerate the signal and send it back out every other port, as networker already stated. Hubs exist at layer 1, and IP addresses exist at layer 3 so an IP address would have no meaning or purpose for the hub.

    The application (be it arp or anything else) is completely ignorant of whether the network is using a hub, a switch, or not even using Ethernet at all. Arp maps an IP address (layer 3) with a MAC address (layer 2), so like IP addresses, ARP has no use in a hub's world.


    I think what you need at this point is a little more reading of the OSI and TCP/IP models. A better understanding of the layers and how they interact will clear this all up for you.
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  20. Member E1or0's Avatar
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    #19
    Networker I understand how Hubs and Switches work back to the main question, why 3 out of 7 computers connected to a hub with the same ip address assign, manually assign can give you a conflict when a hub is not even a layer 3 device, its layer 1 and does not use arp.

    why 3 computers that connects to the same hub cannot communicate do to the fact that they have the same ip address assign, ok put it this way every host HAVE to have an ip address assign differently of course even tough they are connecting to a hub? or assigning an ip address to this hosts at this layer (layer 1) does it really affect the way they can communicate?

    can they communicate without any ip address or they have to have an address assign no matter what?

    I don't know if you understand what I'm trying to expose here

    more simple hosts connected to a hub can they communicate base on their mac address or not ?

    thank you
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  21. Senior Member alan2308's Avatar
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    #20
    Quote Originally Posted by E1or0 View Post
    Networker I understand how Hubs and Switches work back to the main question, why 3 out of 7 computers connected to a hub with the same ip address assign, manually assign can give you a conflict when a hub is not even a layer 3 device, its layer 1 and does not use arp.

    why 3 computers that connects to the same hub cannot communicate do to the fact that they have the same ip address assign, ok put it this way every host HAVE to have an ip address assign differently of course even tough they are connecting to a hub? or assigning an ip address to this hosts at this layer (layer 1) does it really affect the way they can communicate?

    can they communicate without any ip address or they have to have an address assign no matter what?

    I don't know if you understand what I'm trying to expose here

    more simple hosts connected to a hub can they communicate base on their mac address or not ?

    thank you
    With conflicting IP addresses, the computers will still be able to communicate at Layers 1 and 2, they just can't communicate at Layer 3. The hub is in no way stopping them from communicating.
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  22. Went to the dark side.... Moderator networker050184's Avatar
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    #21
    I don't think you understand how ARP works which is why you are confused. Answer these and I think you might get it.

    Q - How does a host get another hosts MAC address?

    A - ARP!

    Q - How does ARP work?

    A - One host sends an ARP request to the IP ADDRESS of the other host to find its MAC.

    Could they communicate without an IP address? Yeah if it was designed to work that way, but it isn't.

    NONE OF THAT HAS ANYTHING TO DO WITH THE HUB!!!!!
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  23. wino burbankmarc's Avatar
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    #22
    All applications operate using TCP/IP. They use IP addresses, not mac addresses.
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  24. Senior Member alan2308's Avatar
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    #23
    Quote Originally Posted by burbankmarc View Post
    All applications operate using TCP/IP. They use IP addresses, not mac addresses.
    Only if you're lucky enough to live in an entirely TCP/IP world. Not everyone gets to pretend IPX (or anything else for that matter) doesn't exist.
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  25. Member E1or0's Avatar
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    #24
    Networker Now I get a clear understanding of everything, I called a collie of mine that had this issue with a client of him he confirmed that there was a router connected to this hub, the device causing the ip conflict was the router it self and not the hub, I always thought he had only a hub and several hosts connected to it, that's why I opened up this thread to clarify my self with this whole idea of the hosts connected to this hub not been able to communicate among them due to this ip conflict message he was receiving when the hub is a layer 1 device that only floods what enters a port to every other as an ( extender or repeater )

    Now I understand what happened to him he never mentioned to me the router lol

    he corrected issue by removing the ip address manually assigned to the 3 hosts and set them up in dhcp, ip addresses conflict corrected

    Thank you again all and sorry for the misunderstanding my friend didn't specified
    Last edited by E1or0; 06-23-2010 at 01:52 AM.
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    #25
    Quote Originally Posted by burbankmarc View Post
    All applications operate using TCP/IP. They use IP addresses, not mac addresses.
    Not all applications operate using TCP/IP. I am sure you know that. c",)
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